This invention relates to compositions and methods useful for removing ink from secondary fiber within an aqueous medium. More particularly, it relates to the use of copolymers of styrene and methacrylic acid as additive agents for aqueous media in which de-inking of secondary fibers take place.
The advent of the recycling of large quantities paper in recent times has provided many benefits, including reduced de-forestation and the preservation of other resources.
As part of the recycling of paper fibers, which recycled paper fibers are commonly referred to as xe2x80x9csecondary fibersxe2x80x9d by those in the art, a key step is the removal of the ink which was formerly bonded to the fibers from the earlier printing present on the paper. For many years, paper was printed with oil-soluble inks which were readily removed by well-established, conventional de-inking procedures. In general terms, such procedures involve mechanically pulping used paper in an aqueous medium which contains surfactant(s), which causes removal of the ink from the paper fibers. The ink may be subsequently removed by washing or flotation.
Attendant with the increased amounts of the recycling of paper have also been several advances in printing, most notably the widespread use of the laser printer and other forms of electrophotographic copying including such methods as xe2x80x9cink-jetxe2x80x9d, non-impact, and xerography. Papers printed in such processes pose additional problems to the recycler which are not found in recycling paper that was printed using oil-soluble or oil-based inks. The additional problems arise from the use of binders in these newer inks which are not found in the oil-soluble inks used previously. Such binders are typically polymeric materials that are thermally bonded to the paper. These types of binders are not readily dispersed by common surfactants like alkylphenol alkoxylates or alkylbenzene sulfonates. Thus, paper produced from recycled paper having electrophotographic printing thereon according to conventional de-inking methods is generally darker than that recycled from paper printed with oil-based inks, because of the much lessened degree of removal of the ink from the substrate.
The present invention provides a copolymer material which is useful in combination with surfactants employed in aqueous systems for de-inking paper fibers which are to be recycled. The copolymers of the invention function synergistically with various surfactants and provide recycled fibers having characteristics substantially similar to virgin fibers used in papermaking. Since the copolymers used in the invention are more hydrophilic and more surface active than those found in the prior art, fibers which are de-inked in accordance with the teachings of the present invention do not agglomerate ink particles but rather disperse and stabilize the ink particles, thus minimizing their tendency to become re-deposited on the fibers.
The present invention is directed at compositions of matter useful in de-inking secondary fibers. A composition according to the invention comprises an anionic form of a styrene-methacrylic acid copolymer, in which the copolymer has a styrene content of any value in the range of 10.00% to 40.00% by weight based upon the total weight of the copolymer. The molecular weight of the copolymer is preferably in the range of 1,000 to 100,000. To maintain charge balance, a composition according to the invention also includes a cation, which is preferably selected from the group consisting of: alkali metal cations, alkaline earth metal cations, ammonium ions, and alkyl-substituted ammonium ions, although any cationic species which does not detract from the performance of a composition in de-inking secondary fibers is a functional equivalent to such cations. A composition according to the invention may also comprise a surfactant, which may be cationic, anionic, or non-ionic, with non-ionic surfactants being preferred. A composition according to the invention also preferably comprises water.
The invention also includes a process for removing ink, toners, and the like from ink-bearing secondary fibers which comprises first providing an aqueous solution of an anionic form of a styrene-methacrylic acid copolymer, which preferably, though not necessarily, contains a surfactant. A fiber suspension is formed by contacting secondary fibers with said composition and maintaining such contact for an effective amount of time to cause the ink on said secondary fibers to be removed from said fibers. Finally, the ink is removed from the suspension by a method which may include flotation or washing.
The present invention relates to compositions useful for removing inks from secondary fibers. Compositions according to the invention comprise a water-soluble form of styrene-methacrylic acid copolymer in which the copolymer has a styrene content between about 10 and 40 percent by weight based upon the total weight of the polymer. The preferred compositions according to the invention are aqueous solutions of an alkali metal salt of a copolymer as herein described. The copolymer can be used alone, or, more preferably, in combination with an alkoxylated fatty alcohol and/or an alkoxylated castor oil surfactant.
The preparation of styrene/methacrylic acid copolymers is straightforward and is known in the art. One method for preparing such copolymers useful in the present invention involves fitting a 3-necked 1L flange flask with a mechanical stirrer, heating mantle, thermometer, reflux condenser, addition inlet, and provision for maintaining an inert atmosphere within the reaction vessel, such as a nitrogen inlet. The flask is charged with three hundred thirty six (336) grams of isopropanol and one hundred twelve (112) grams of water. Heating is commenced under stirring and slow nitrogen sweep until a gentle reflux is achieved, at about 80 deg. Centigrade. A first stream comprising eighty (80) milliliters of a 5% aqueous sodium persulphate solution was slowly added to the contents of the refluxing contents of the flask simultaneously with a second stream comprising a liquid mixture of 70.4 grams of styrene and 105.4 grams of methacrylic acid, over the course of about 2 hours. Following the addition, the temperature was maintained at reflux for an additional 2 hours to ensure complete reaction. Then, an additional ten (10) milliliters of 22% sodium persulphate was added, and the temperature maintained at reflux for one additional hour to provide a styrene/methacrylic acid copolymer.
To prepare a water-soluble salt of a copolymer produced as per the above, namely the sodium salt, the flask from the above was set up for distillation by affixing a head and condenser thereto. The flask is heated until the azeotrope of isopropanol and water begins to distill, and then two hundred thirteen (213) grams of a 23% (wt.) aqueous solution of sodium hydroxide is slowly added to the flask during the distillation at a rate which is approximately equal to the rate at which the azeotrope is being distilled. The temperature of the contents of the flask are monitored, and when the temperature reaches 100-105 deg., the flask is allowed to cool to 50 degrees centigrade and the pH is adjusted to a level between about 8 and 10 using aqueous NaOH, and to a total solids content of between about 30 and 35% (wt.) as determined by evaporation of all of the water from a sample of known weight and dividing the weight of the solids remaining by the total initial weight and converting to a percentage by multiplication by 100. This procedure affords an aqueous solution comprising the sodium salt of styrene/methacrylic acid copolymer, to which may be optionally added a surfactant in order to provide a de-inking composition according to the invention.
Although the water-soluble salt of the copolymer whose preparation is described above as being the sodium salt as formed by the addition of aqueous sodium hydroxide in the final step in which the alcohol is removed by distillation, other basic substances which produce a water-soluble polymer are suitable as employment as neutralizing agents herein. Such basic substances include without limitation alkaline aqueous solutions or suspensions of other soluble metal cations, metal oxides, carbonates, etc., including without limitation, basic carbonates of any of the alkali metals, alkaline earth metals, monovalent iron, the basic oxides of any of the alkali metals or monovalent iron, ammonia, or alkyl-substituted amines including primary, secondary, and tertiary amines provided that a solution of the copolymer results after the admixture and heating. In cases where suspensions of oxides are used, a longer heating time may be necessary to effectuate solution, depending upon the particle size of the basic substance.
In the above-described method for preparing a styrene-methacrylic acid copolymer the styrene/methacrylic acid ratio is about 40:60. Copolymers of styrene and methacrylic acid having other ratios are also useful herein as the copolymer component from which a de-inking composition according to the present invention may be formed. The water-soluble forms of copolymers of styrene-methacrylic acid having any content of styrene in the range of 10.0% to 45.0%, by weight based upon the total weight of the styrene-methacrylic acid polymer, including every hundredth percentage therebetween, are suitable for use in the present invention. These polymers having varied amounts of styrene and methacrylic acid are made by altering the relative amounts of each of the components in the second stream referred to in the preparatory method above. For example, when a copolymer having a styrene to methacrylic acid ratio of 30:70 is desired, the second stream comprises 52.70 grams of styrene and 123.06 grams of methacrylic acid. When a copolymer having a styrene to methacrylic acid ratio of 20:80 is desired, the second stream comprises 31.15 grams of styrene and 140.61 grams of methacrylic acid.
The molecular weight of the copolymers produced according to a procedure such as that described above in accordance with the invention may be any molecular weight in the range of about 1,000 to about 100,000, with molecular weights having any value in the range of 1,500 to 50,000 being preferred, and with molecular weights having any value in the range of about 2,000 to about 30,000 being most preferred. The molecular weight of the final copolymer is controlled by the concentration of the initiator and the chain transfer agent, as is well known to those skilled in the art of providing copolymers produced by this method. In the present invention, the preferred chain transfer agent is isopropanol and the preferred initiator is persulfate ion. Other functionally equivalent chain transfer agents and initiators known to those skilled in the art are useful in preparing the polymers described herein.
The present invention provides a compositions useful for de-inking secondary fibers, which compositions comprise an aqueous solution of a water-soluble form of a copolymer of styrene and methacrylic acid described above. An aqueous composition according to the present invention may also optionally include a surfactant. Any surfactant is suitable for use as an optional ingredient for inclusion in a composition according to the invention, including anionic surfactants, non-ionic surfactants, and cationic surfactants. Surfactants are well known in the chemical arts to comprise a class of materials whose molecular structures include both a hydrophilic portion and a hydrophobic portion. In addition, a surfactant molecule as a whole may carry a positive charge, negative charge, or may be electrically neutral, as is known to those skilled in the art. The number and type of surfactants known in the art is great indeed. It is most preferred that a surfactant used in a composition according to the present invention is a non-ionic surfactant. Alkoxylated oils are one class of non-ionic surfactant which are produced by reacting an alkylene oxide with an oil in the presence of a base catalyst, as such is well-known to those skilled in the surfactant arts. Generally, to produce such materials, one may use a tri-glyceride oil derived from any vegetable or animal matter in combination with one or more alkylene oxides. In cases where more than one alkylene oxide is used in the alkoxylation of an oil, the molecular structure of the resulting alkoxylated oil will contain two different alkylene oxide units. An especially preferred non-ionic surfactant suitable for use in the present invention is available from Huntsman Petrochemical Corporation of Austin, Tex. under the designation xe2x80x9cG-5000xe2x80x9d. The amount of surfactant component present in a composition according to the invention in any amount between 0.05% and 2.00% percent by weight based upon the total weight of the fiber to be treated.
A de-inking solution according to the present invention may be used at any temperature during its use between just above freezing temperature to about 95 degrees centigrade, with about 25 degrees centigrade being preferred. The concentration of the copolymer component in a de-inking solution according to the present invention is preferably between 0.01% and 2.00% by weight based upon the total weight of the dry fiber being de-inked. More preferably, this amount is between 0.04% and 1.5%, with about 1.00% being most preferable.